Before the opening credits, the bad guys shooting at the Aston Martin are blown away by a high pressure stream of water. The car would have required a water tank capable of holding over 200 gallons, which would weigh well over a ton.
Yes many, if not most, of Bond's gadgets could not exist in real life. It's called suspension of disbelief. I'm not sure this warrants it's own thread.
Funny, the Bell Rocket Belt, used just moments earlier would "seem" more unbelievable but it does exist and works in real life. I suspect the same Hydrogen Peroxide/Silver system used to create steam for the Bell Rocket Belt, could have been used instead of the "water cannon". It's output would most likely have a higher velocity, plus the steam would have been more likely to chase someone off.
According to the extras on my DVD the jet pack works fine. The only problem is you can't just take it off as 007 does. It would be so hot it would take the skin off your hands.
My favourite is the story about the rebreather. Apparently the US Navy rang the special effects department and asked how long it could be used for.
Came the answer :"How long can you hold your breath" You would love that to be true